Inert gas purging system for an orc heat recovery boiler

ABSTRACT

In one embodiment, a system includes a valve system switchable between a waste heat recovery position configured to direct incoming exhaust gas through an interior volume of an exhaust section of an engine and a bypass position configured to direct the incoming exhaust gas through a bypass duct to bypass a heat recovery boiler disposed within the interior volume. The system also includes an inert gas purging system configured to inject an inert gas into the interior volume to displace residual exhaust gas from the interior volume.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to waste heat recoverysystems employing boilers, and more specifically, to inert gas purgingsystems for heat recovery boilers.

Waste heat recovery systems may be employed to recover low-grade heat,such as heat with a temperature below approximately 500° C., fromindustrial and commercial processes and operations. For example, wasteheat recovery systems may be employed to recover low-grade heat from hotexhaust gases produced by gas turbines. Waste heat recovery systems thatimplement an Organic Rankine Cycle (ORC) by circulating an organicworking fluid may be particularly efficient at recovering low-grade heatdue to the relatively low phase change enthalpies of organic workingfluids.

BRIEF DESCRIPTION OF THE INVENTION

In a first embodiment, a system includes a valve system switchablebetween a waste heat recovery position configured to direct incomingexhaust gas through an interior volume of an exhaust section of anengine and a bypass position configured to direct the incoming exhaustgas through a bypass duct to bypass a heat recovery boiler disposedwithin the interior volume. The system also includes an inert gaspurging system configured to inject an inert gas into the interiorvolume to displace residual exhaust gas from the interior volume.

In a second embodiment, a system includes a heat recovery boilerconfigured to absorb heat directly from exhaust gas within an exhaustsection of an engine to heat an organic working fluid within the heatrecovery boiler, an expander configured to expand the heated organicworking fluid, a condenser configured to condense the expanded organicworking fluid, a pump configured to direct the condensed organic workingfluid to the heat recovery boiler, a sensor configured to detect a leakof the organic working fluid from the heat recovery boiler, and an inertgas purging system configured to inject inert gas into the exhaustsection in response to detection of the leak.

In a third embodiment, a method includes detecting a leak of an organicworking fluid from a heat recovery boiler into an interior volume of anexhaust section of an engine, setting a valve to a bypass position todirect incoming exhaust gas to bypass the interior volume of the exhaustsection in response to detecting the leak, and injecting an inert gasinto the interior volume to displace residual exhaust gas from theinterior volume in response to detecting the leak.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic flow diagram of an embodiment of a powergeneration system that may employ an inert gas purging system within awaste heat recovery system;

FIG. 2 is a schematic flow diagram of the waste heat recovery system ofFIG. 1 depicting an embodiment of an inert gas purging system;

FIG. 3 is a schematic flow diagram of the waste heat recovery system ofFIG. 2 operating in the bypass mode; and

FIG. 4 is a flowchart depicting an embodiment of a method for purgingexhaust gas from a heat recovery boiler.

DETAILED DESCRIPTION OF THE INVENTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The present disclosure is directed to waste heat recovery systems thatemploy inert gas purging systems for heat recovery boilers. The wasteheat recovery systems may recover low-grade heat from a system, such asa gas turbine, by implementing an Organic Rankine Cycle (ORC) with anorganic working fluid, such as a hydrocarbon fluid or refrigerant.Rather than transferring heat to the organic working fluid through anintermediate fluid, such as oil, the present systems may employ a“direct” heat recovery boiler that transfers heat directly from the gasturbine exhaust gas to the working fluid. According to certainembodiments, the heat recovery boiler, which circulates the workingfluid, may be disposed directly in the path of the exhaust gas withinthe exhaust section of the gas turbine. Placing the heat recovery boilerdirectly in the path of the exhaust gas, rather than using a secondaryloop to transfer heat between the exhaust gas and the waste heatrecovery system, may increase the overall efficiency of the waste heatrecovery system, as well as reducing capital and/or operational costs.

To protect the gas turbine exhaust section and the waste heat recoverysystem in the event of a leak in the heat recovery boiler, the powergeneration system may employ a purging system for the heat recoveryboiler. According to certain embodiments, the purging system may beenabled upon detection of a leak in the heat recovery boiler. Thepurging system may redirect the flow of exhaust gases so that theexhaust gases bypass the heat recovery boiler. Further, the purgingsystem may inject an inert gas into the exhaust gas duct to purgeresidual exhaust gases from the exhaust duct. The inert gas also maycool the heat recovery boiler and dilute any leaking fluid, therebyextinguishing and/or inhibiting flames within the exhaust duct.

FIG. 1 depicts an embodiment of a power generation system 10 that mayemploy a heat recovery boiler purging system. The power generationsystem 10 includes an engine, such as a gas turbine engine 12, thatgenerates waste heat that may be recovered by a waste heat recoverysystem 16. As may be appreciated, the gas turbine engine 12 is providedas one example of an engine that produces waste heat, and is notintended to be limiting. In other embodiments, the waste heat recoverysystem described herein may be employed to recover heat from other typesof engines that generate waste heat. For example, in other embodiments,the waste heat recovery system 16 may recover heat from a reciprocatingengine, or other suitable engine that produces waste heat.

As shown in FIG. 1, the gas turbine engine 12 combusts fuel (e.g. aliquid or gas fuel) to drive a first load 14. The power generationsystem 10 also includes a waste heat recovery system 16 that recoverslow-grade heat from the gas turbine to drive a second load 18. Accordingto certain embodiments, the first and second loads 14 and 18 may beelectrical generators for generating electrical power. However, in otherembodiments, the types of loads driven by the power generation system 10may vary.

The gas turbine engine 12 includes an air intake section 20, acompressor 22, a combustor section 24, a turbine 26, and an exhaustsection 28. The turbine 26 is coupled to the compressor 22 via a shaft30. Air 32 may enter the gas turbine engine 12 through the intakesection 20 and flow into the compressor 22 where the air may becompressed to provide compressed air 34 to the combustor section 24.Within the combustor section 24, the compressed air 34 may mix with fuelin a fuel-to-air ratio that facilitates combustion of the fuel toproduce combustion gases 36. According to certain embodiments, thecombustor section 24 may include multiple combustors disposed annularlyaround the shaft 30.

From the combustor section 24, the hot combustion gases 36 may flowthrough the turbine 26 to drive the compressor 22 and/or the first load14 via the shaft 30. For example, the combustion gases 36 may applymotive forces to turbine rotor blades within the turbine 26 to rotatethe shaft 30. After flowing through the turbine 26, the hot combustiongases may exit the gas turbine engine 12 as exhaust gases 38 that flowthrough the exhaust section 28 to exit the gas turbine engine 12.

As the exhaust gases 38 flow through the exhaust section 28, the exhaustgases 38 may flow through an heat recovery boiler 40 that may absorbheat from the exhaust gases 38 to produce cooled exhaust gases 42. Theheat recovery boiler 40 is located directly in the flow path of theexhaust gases 38 so that the exhaust gases 38 may transfer heat directlyto a working fluid flowing through the heat recovery boiler 40. Thecooled exhaust gases 42 may then exit the exhaust section 28 and may bedirected through ductwork 43 to a stack 44 where the gases may be ventedto the atmosphere.

As described further with respect to FIG. 2, the exhaust section 28 alsomay include a bypass duct 46 that allows the exhaust gases 38 to exitthe exhaust section 28 without flowing past the heat recovery boiler 40.The bypass duct 46 may be employed to remove exhaust gases 38 from theexhaust section 28 if the heat recovery boiler 40 develops a leak thatmay expose combustible organic working fluid from the heat recoveryboiler 40 to the exhaust gases 38. When the bypass mode is enabled, theexhaust gases 38 may be directed through the bypass duct 46 to exit theexhaust section 28 as bypass exhaust gases 48 that have bypassed theheat recovery boiler 40. The bypass exhaust gases 48 may be directed tothe stack 44 where the gases may be vented to the atmosphere. As shown,both the bypass exhaust gases 48 and the cooled exhaust gases 42 may bedirected to the same stack 44. However, in other embodiments, the bypassexhaust gases 48 and the cooled exhaust gases 42 may be directed toseparate stacks.

As the exhaust gases 38 flow through the heat recovery boiler 40disposed within the exhaust gas path of the exhaust section 28, the hotexhaust gases 38 may transfer heat to a working fluid flowing throughthe heat recovery boiler 40 within a working fluid loop 50. According tocertain embodiments, the heat recovery boiler 40 may be a fin and tubeheat exchanger that allows the working fluid to be circulated within theworking fluid loop 50 directly in the path of the exhaust gases 38.Accordingly, the exhaust gases 38 may transfer heat directly to theworking fluid circulating within the waste heat recovery system 16,rather than transferring heat through an intermediate loop, such as anoil loop.

According to certain embodiments, the waste heat recovery system 16 maycirculate an organic working fluid within the working fluid loop 50 torecover waste heat from the exhaust gases 38. Any suitable organicworking fluid, such as a hydrocarbon fluid or refrigerant, may beemployed. The use of an organic working fluid may be particularly wellsuited to the waste heat recovery loop 50 due to the relatively lowphase change enthalpy of the organic working fluid. According to certainembodiments, the organic working fluid may be an organic, high molecularmass, fluid that has a higher vapor pressure and lower criticaltemperature than water.

As the working fluid flows through the heat recovery boiler 40, theworking fluid may absorb heat from the exhaust gases 38 causing all, ora substantial portion of the working fluid to change from a liquid phaseto a vapor phase. The heated working fluid may then flow to an expandergenerator set 52 where the working fluid may be expanded to drive thesecond load 18. For example, the expander generator set 52 may includean expander that may be coupled to a generator to produce electricityfrom the expansion of the heated working fluid. From the expandergenerator set 52, the working fluid may flow to a condenser 54 where theworking fluid may be condensed. According to certain embodiments, thecondenser 54 may be an air-cooled heat exchanger. However, in otherembodiments, any suitable type of condenser may be employed.

The condensed working fluid may then flow through a pump 58 that returnsthe working fluid to the heat recovery boiler 40 where the process maybegin again. In other embodiments, additional equipment, such as valves,temperature and/or pressure sensors or transducers, receivers, and thelike, may be included in the waste heat recovery system 16. For example,in certain embodiments, a recuperator or preheater may be includedupstream from the heat recovery boiler 40 to preheat the working fluidbefore it enters the heat recovery boiler 40. Further, the waste heatrecovery system 16 may be installed as part of a new power generationsystem 10 and/or may be retrofit into an existing power generationsystem 10. For example, in certain embodiments, an existing gas turbine12 may be retrofitted with a waste heat recovery system 16 that disposesa heat recovery boiler 40 in the exhaust gas section 28.

As shown in FIG. 1, the heat recovery boiler 40 is located within theexhaust section 28 directly in the flow path of the hot exhaust gas 38.The direct transfer of heat from the exhaust gas to the waste heatrecovery system 16 may increase the overall efficiency of the waste heatrecovery system 16 when compared to a system using an intermediate loopto indirectly transfer heat from the exhaust gas to the waste heatrecovery system. Further, the elimination of a secondary loop may reducecapital and/or operational costs. However, due to the potentialflammability of the organic working fluid, it may be desirable to removeexhaust gases 38 from the exhaust section 28 during standstill of thesystem and/or in the event of a leak in the heat recovery boiler 40 thatmay allow the working fluid to leak from the heat recovery boiler intothe exhaust section 28. Accordingly, FIGS. 2 and 3 depict an inert gaspurging system that may be employed to remove and/or to dilute exhaustgases 38 from the exhaust section 28.

As shown in FIG. 2, the exhaust gases 38 may flow through an opening 58to enter an interior volume 60 of the exhaust section 28, as generallyshown by arrows 61. The heat recovery boiler 40 may be located withinthe interior volume 60 in the flow path of the exhaust gases 38. Theheat recovery boiler 40 includes finned tubes 62 in which the workingfluid is circulated. According to certain embodiments, the finned tubes62 may be disposed generally perpendicular to the flow of the exhaustgas 38 through the interior volume 60 to promote good heat transfer fromthe exhaust gases 38 to the working fluid circulating within the finnedtubes 62.

After the exhaust gases 38 flow through the heat recovery boiler 40, thecooled exhaust gases 42 may exit the exhaust section 28 and enter thestack 44 through an inlet 63. As discussed above, because the workingfluid circulating within the finned tubes 62 may be potentiallyflammable, it may be desirable to remove the exhaust gases 38 from theinterior volume 60 in the event of a leak in the finned tubes 62.Accordingly, in the event of a leak, rather than directing the exhaustgases 38 through the opening 58 to the interior volume 60, the exhaustgases 38 may be directed through an opening 64 to flow through thebypass duct 46, as shown generally by arrows 65 in FIG. 3.

To redirect the flow of the exhaust gases 38 through the bypass duct 46,a system of one or more valves 66 may be employed, which are switchablebetween a waste heat recovery position as shown in FIG. 2 and a bypassposition as shown in FIG. 3. The valves 66 may include any type of flowdirecting, switching, and/or throttling devices that may be switchedbetween positions to permit flow in one position and to restrict flow inanother position. According to certain embodiments, the valves 66 mayinclude baffles or dampers; however, in other embodiments, any suitabletype of valves may be employed.

In the waste heat recovery position, the valve 66 may be positioned todirect the exhaust gases 38 through the interior volume 60, as shown inFIG. 2. In the bypass position, the valve 66 may be positioned to directthe exhaust gases 38 through the bypass duct 46, as shown in FIG. 3.Although the valve 66 is shown in FIGS. 2 and 3 as a single baffle, inother embodiments, a system of two or more baffles and/or dampers may beemployed to switch the flow of the exhaust gases between the interiorvolume 60 and the bypass duct 46.

In the waste heat recovery mode shown in FIG. 2, the valve 66 ispositioned over the opening 64 to allow the exhaust gases 38 to flowthrough the opening 58 into the interior volume 60 where the exhaustgases 38 may flow through the heat recovery boiler 40. A flap 69 may beopened within inlet 63 to allow exhaust gases to flow from the interiorvolume 60 into the stack 44 through the inlet 63. Further, a flap 71 maybe closed within the bypass duct 46 to impede the flow of exhaust gasesinto the bypass duct 46 from the stack 44. The flaps 69 and 71 may bepositioned within the ductwork 43, within the stack inlets 63 and 67, orwithin the bypass duct 46 and the exhaust section 28. Further, incertain embodiments, the flaps 69 and 71 may be omitted.

When the bypass mode is enabled as shown in FIG. 3, the valve 66 may bepositioned over opening 58 to allow the exhaust gases 38 to flow throughthe opening 64 into the bypass duct 46. Accordingly, in the bypass mode,the exhaust gases 38 may bypass the heat recovery boiler 40 by flowingthrough the bypass duct 48 and into the stack 44 through an inlet 67. Inthe bypass mode, the flap 71 may be opened to allow the exhaust gases toflow from the bypass duct 46 to the stack 44 through inlet 67. Further,the flap 69 may be closed to impede the flow of exhaust gases from thestack 44 into the interior volume 60 through the inlet 63.

The bypass duct 46 may be employed when a leak is detected in the finnedtubes 62 of the heat recovery boiler 40. Accordingly, one or moresensors 68 may be employed to detect a leak in the finned tubes 62. Forexample, in embodiments where the working fluid is a hydrocarbon fluid,the sensor 68 may measure the level of hydrocarbons in the exhaust gasexiting the interior volume 60. An increased level of hydrocarbons mayindicate a leak within the finned tubes 62. In another example, thesensor 68 may be designed to detect presence of a flame in or around theheat recovery boiler 40, such as by measuring ultraviolet light. Thepresence of a flame may indicate a leak within the finned tubes 62. Inyet another example, multiple sensors 68, such as multiple hydrocarbonsensors, multiple flame detection sensors, or combinations thereof, maybe employed. Further, in other embodiments, the sensor 68 may bedesigned to measure other parameters indicative of the composition ofthe exhaust gases 38. According to certain embodiments, the sensor 68may be located in the inlet 63 to the stack 44. However, in otherembodiments, the sensor 68 may be positioned within the interior volume60.

The sensor 68 may be communicatively coupled to a controller 70 that maybe used to change the position of the valve 66. For example, thecontroller 70 may receive an input, such as a hydrocarbon level, fromthe sensor 68 that indicates that a leak is present in the finned tubes62. In response to receiving the input, the controller 70 may send acontrol signal to the valve 66 to move the valve to close opening 58, asshown in FIG. 3, thereby directing the exhaust gases 38 through theopening 64 and into the bypass duct 46. According to certainembodiments, the controller 70 may include an analog to digital (A/D)converter, a microprocessor, a non-volatile memory, and an interfaceboard, among components. However, in other embodiments, rather thanbeing electronically controlled by controller 70, the valve 66 may bemechanically and/or manually controlled. For example, in certainembodiments, the controller 70 may produce an output, such as an alarm,that indicates that the valve 66 should be moved, for example by anoperator, to close the opening 58.

The controller 70 also may govern operation of an inert gas injectionsystem 72 that may be used to purge residual exhaust gases 38 from theinterior volume 60 after the valve 66 has been moved to the bypassposition. The inert gas injection system 72 may include an inert gassupply 74, such as one or more high pressure gas cylinders, whichsupplies inert gases for the inert gas injection system 72. As usedherein, the term “inert gases” shall mean any gas or mixture of gasessuitable to suppress combustion, prevent explosion, or extinguish aflame, primarily by dilution and/or displacement of oxygen in theexhaust gas. According to certain embodiments, the inert gases mayinclude nitrogen and/or carbon dioxide.

Piping 76 may be used to direct the inert gases from the inert gassupply 74 into the interior volume 60. A valve 78 may be included withinthe piping 76 to regulate the flow of the inert gases from the tank 74into the interior volume 60. For example, the valve 78 may be closedwhen the system is operating in a waste heat recovery mode to preventthe inert gases from entering the interior volume 60 and may be openedto allow the inert gases to enter the interior volume 60 when the systemis operating in the bypass mode. Further, in certain embodiments, thevalve 78 may be employed to increase and decrease the flow rate of theinert gases into the interior volume 60. Although only one valve 78 isshown in FIGS. 2 and 3, in other embodiments, a system of multiplevalves 78 may be included within the piping 76.

The controller 70 may govern the operation of the inert gas injectionsystem 72 through the valve 78. According to certain embodiments, thecontroller 70 may open the valve 78 in response to detecting a leak toallow the inert gases to enter the interior volume 60. The inert gasesmay enter the interior volume through one or more nozzles 79 that mayinject the inert gases into the interior volume 60 from the piping 76.According to certain embodiments, the nozzles 79 may allow the inertgases to be injected into the interior volume 60 at relatively high flowrates. Further, the nozzles 79 may be located along the top, bottom,and/or sides, as well as around the exhaust gas inlet area, of theinterior volume 60.

As the inert gases enter the interior volume 60, the inert gases maydisplace residual exhaust gases 38 within the interior volume 60 causingthe residual exhaust gases to exit the interior volume 60 and enter thestack 44 through the inlet 63. Accordingly, when bypass mode is enabled,the flap 69 may remain open for a certain period of time to allow theresidual exhaust gases to exit the interior volume 60 through the inlet63. After the residual exhaust gases have exited the interior volume 60,the flap 69 may be closed, as shown in FIG. 3, to inhibit flow ofexhaust gases from the stack 44 into the interior volume 60 through theinlet 63. The inert gases also may cool the finned tubes 62 and theinterior volume 60, thereby lowering the pressure and temperature inwithin the interior volume 60. Further, the inert gases may diluteoxygen and hydrocarbon vapors within the interior volume 60, therebyextinguishing any flames that are present within the interior volume 60and/or inhibiting flames and/or explosion within the exhaust section 28.

After valve 78 has been opened to allow the inert gases to enter theinterior volume 60, the controller 70 may stop operation of the pump 58that circulates the working fluid through the heat recovery boiler 40.When the pump 58 is stopped, the working fluid may evaporate from theheat recovery boiler 40 and collect within the working fluid loop 50.Accordingly, additional working fluid may be inhibited from leaking intothe interior volume 60 through the heat recovery boiler 40.

FIG. 3 depicts the exhaust section 28 when the system is in the bypassmode to direct the exhaust gases 38 through the bypass duct 46. As shownin FIG. 3, the valve 66 is positioned over the opening 58 to close theopening 58 and allow the exhaust gases 38 to flow through the opening 64the bypass duct 46. Accordingly, incoming exhaust gases 38 will bedirected to the bypass duct 46 rather than to the interior volume 60that houses the heat recovery boiler 40. As shown in FIGS. 2 and 3, asingle valve 66 may be moved to close off opening 58 and allow flowthrough the opening 64. However, in other embodiments, a system ofmultiple valves 66, such as multiple baffles or dampers, among others,may be employed to switch the system between a waste heat recovery modewhere the exhaust gases enter the interior volume 60 and a bypass modewhere the exhaust gases enter the bypass duct 46.

FIG. 4 is a flowchart depicting a method 82 that may be used to purgethe interior volume 60 of exhaust gases 38. The method 82 may begin bydetecting (block 84) a leak in the heat recovery boiler 40. For example,as shown in FIG. 2, a sensor 68 may detect increased levels ofhydrocarbons and/or the presence of a flame. The sensor 68 may provide asignal indicating the level of hydrocarbons to the controller 70 (FIG.2). The controller 70 may then compare the level to a predeterminedthreshold or rate of change to determine if a leak is present. In otherembodiments, the sensor 68 may determine whether a leak is present andmay provide a control input indicating a leak to the controller 70.

In response to detecting a leak, the controller 70 may set (block 86)the valve to the bypass position. For example, as shown in FIG. 3, thecontroller 70 may switch the valve to close off opening 58 and directthe exhaust gases 38 into the bypass duct 46 through the opening 64. Inanother embodiment, two or more baffles may be used, and in theseembodiments, the controller 70 may move one baffle to close the opening58 and may move another baffle to open the opening 64.

After setting the valve 66 to the bypass position, the controller 70then may inject (block 88) purge gas into the interior volume 60. Forexample, the controller 70 may activate the inert gas purging system byopening valve 78 to allow the inert gases to flow into the interiorvolume 60 through the nozzles 79. The inert gases may then purgeresidual exhaust gases 38 from the interior volume 60 by displacing theresidual exhaust gases 38 from the interior volume 60 to the stack 44through the inlet 63. As noted above with respect to FIG. 2, the inertgases also may reduce the temperature within the interior volume 60,thereby reducing the occurrence of fire and/or extinguishing any flamesthat may be present within the interior volume 60. The controller 70also may stop (block 90) operation of the pump 56 (FIG. 1) thatcirculates the working fluid through the heat recovery boiler 62.Stopping the pump may inhibit additional working fluid from entering theinterior volume 60 through the heat recovery boiler 40.

After the interior volume 60 has been purged of the exhaust gases 38,repairs may be conducted to repair any leaks within the heat recoveryboiler 40. For example, the finned tubes 62 may be repaired or replaced.After the repairs have been completed, the valve 66 may be reset to thewaste heat recovery position, as shown in FIG. 2, which allows theincoming exhaust gases 38 to again enter the interior volume 60.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

1. A system comprising: a valve system switchable between a waste heatrecovery position configured to direct incoming exhaust gas through aninterior volume of an exhaust section of an engine and a bypass positionconfigured to direct the incoming exhaust gas through a bypass duct tobypass a heat recovery boiler disposed within the interior volume; andan inert gas purging system configured to inject an inert gas into theinterior volume to displace residual exhaust gas from the interiorvolume.
 2. The system of claim 1, wherein the inert gas purging systemcomprises an inert gas valve system configured to selectively enable anddisable a flow of the inert gas from an inert gas supply to the interiorvolume.
 3. The system of claim 1, wherein the inert gas purging systemcomprises flow nozzles configured to be mounted within the interiorvolume to inject the inert gas into the interior volume.
 4. The systemof claim 1, comprising a controller configured to move the valve systemto the bypass position and to activate the inert gas purging system inresponse to detection of a leak in the heat recovery boiler.
 5. Thesystem of claim 4, comprising a sensor configured to detect an amount ofan organic working fluid within the interior volume to detect the leakin the heat recovery boiler.
 6. The system of claim 1, wherein the heatrecovery boiler is configured to circulate an organic working fluid froma waste heat recovery system.
 7. A system comprising: a heat recoveryboiler configured to absorb heat directly from exhaust gas within anexhaust section of an engine to heat an organic working fluid when theorganic working fluid is present within the heat recovery boiler; anexpander configured to expand the heated organic working fluid; acondenser configured to condense the expanded organic working fluid; apump configured to direct the condensed organic working fluid to theheat recovery boiler; a sensor configured to detect a leak of theorganic working fluid from the heat recovery boiler; and an inert gaspurging system configured to inject inert gas into the exhaust sectionin response to detection of the leak.
 8. The system of claim 7, whereinthe heat recovery boiler comprises a fin and tube heat exchanger.
 9. Thesystem of claim 7, wherein the expander comprises an expander generatorset configured to generate electricity through expansion of the heatedorganic working fluid.
 10. The system of claim 7, wherein the condensercomprises an air-cooled heat exchanger.
 11. The system of claim 7,comprising a controller configured to activate the inert gas purgingsystem in response to detection of the leak.
 12. The system of claim 11,wherein controller is configured to stop the pump in response todetection of the leak.
 13. The system of claim 7, comprising a valvesystem configured to be mounted in the exhaust section and to beswitchable between a waste heat recovery position configured to directthe exhaust gas through the interior volume and a bypass positionconfigured to direct the exhaust gas through a bypass duct to bypass theheat recovery boiler.
 14. A method comprising: detecting a leak of anorganic working fluid from a heat recovery boiler into an interiorvolume of an exhaust section of an engine; setting a valve to a bypassposition to direct incoming exhaust gas to bypass the interior volume ofthe exhaust section in response to detecting the leak; and injecting aninert gas into the interior volume to displace residual exhaust gas fromthe interior volume in response to detecting the leak.
 15. The method ofclaim 14, wherein detecting a leak comprises detecting an increase in alevel of hydrocarbons exiting the interior volume.
 16. The method ofclaim 14, wherein detecting a leak comprises receiving data indicativeof the leak from a sensor disposed within an exhaust gas stack or withinthe interior volume.
 17. The method of claim 14, wherein setting a valveto a bypass position comprises moving the valve to open an inlet to abypass duct and to close an inlet to the interior volume.
 18. The methodof claim 14, wherein setting a valve to a bypass position comprisesmoving a system of valves to open an inlet to a bypass duct and to closean inlet to the interior volume.
 19. The method of claim 14, whereininjecting an inert gas into the interior volume comprises opening avalve connected to a supply of the inert gas to allow the inert gas toflow into the interior volume.
 20. The method of claim 14, comprisingstopping a pump that circulates the organic working fluid through theheat recovery boiler in response to detecting the leak.